If I have a contractor come and redo my kitchen, and I am quoted a certain time frame then I will blame him when things do not happen on time - even if his supplier couldn't deliver the cabinets in time, or the hardware store was out of joint compound.

It's a sucky situation, and I feel for Heroku - and I blame AWS personally - but when it comes to the final customer, then as a service provider it's only right to take blame.